Future prospects and needs for nuclear structure studieswith higher intensity stable beams

F. Azaiez (IPN-Orsay)NUPECC Meeting – Frascati ( december 2003)

i) Using stable beams facilities and new generation of detection techniques, the low energy nuclear physics community has proven to be impressively productive with new results and future perspectives!ii) Some of the key questions in the nuclear structure field are and will remain for the coming 10 years well addressed using the state of the art detection systems and higher intensity stable beams!

SHE: Where the isle of stability is located? what are the corresponding shell

effects ?

114 ? 120 ? 126 ?

184

28

8

20

50

82

82

50

288

20

126

Well identified research program:-Systematic search of SHE-Study of the ‘stabilizing’ shell structure -Study of complete fusion - fission processes

• Theoretical predictions !

- "macroscopic-microscopic«  Calculations

Z=114 et N=184

- relativistic Mean field calculations

Z=120/126 et N=184

-Hartree-Fock (Skyrme ) Calculations

Z=126 et N=184

testing spin-orbit and more generally

effective interactions at the extreme!

• Experimental Thechniques

Filter

NSHE . Ni . Nt . f . d

Ni : number of incident ions

beam intensity

Nt: number of target ions

f : selection efficiency ~ 65%

d : detection efficiency ~ 85%

High Intensity beams are essential!

Systematic search: approaching the limit ?

10-5

10-6

10-7

10-8

10-9

10-10

10-11

10-12

10-13

10-14

10-15102 104 106 108 110 112 114 116 118 120

1b

1nb

1pb

1fb

Charge Z

/

barn

208Pb209Bi

production of element 112:

70Zn + 208Pb 277112 + 1n ~ 0.5 pb

I = 0.35 pA (2.1 1012pps) 1 evt./19 jours

production of element 114:

76Ge + 208Pb 278114 + 1n ~ 0.1 pb 1 evt./3 mois

production of element 116:

82Se + 208Pb 289116 + 1n ~ 0.05 pb 1 evt./15 mois

production of element 118:

86Kr + 208Pb 293118 + 1n ~ 0.01 pb 1 evt./6 ans

I = 200 pA 6 evt./jour

I = 200 pA 1 evt./jour

I = 200 pA 1 evt./5 joursS. H

ofm

ann,

Rep

. Pro

g. P

hys.

61(

1998

)639

. Status: Z=112 (GSI),

Z=114,116 (Dubna)-to be confirmed!

Need for dedicated high intensity stablebeams (few 100 pµA) and target developments!

200 pµA = 1.2 1015 pps

1 pµA = 6.3 1012 pps

Spectroscopy to probe Shell Structure of Super-heavy Nuclei

82

114

2d3/2

3s1/2

1h9/2

1i13/2

2f7/2

2p3/2

2f5/2

108

126

1j15/2

-0.3 0 0.3 0.6déformation 2

What is the sequence of single particle states and what are the resulting energy gaps in the super-

heavy nuclei?

Spectroscopic Studies

Prompt and e-spectroscopy of 254No208Pb(48Ca,2n)254No ~ 2.0 b

F.P. Heberger et al. Eur. Phys. J A12(2001)57M. Leino et al. Eur. Phys. J A6(1999)63

JYFL

I~10pnA

- Prompt and e- spectrscopy (in-beam)- Decay studies (off-beam)

décay study of 255Rf208Pb(50Ti,3n)255Rf ~ 0.2 nb

• Apply for Super-Heavy Elements

Spectroscopy of nuclei up to Z=108 and N=162

In the future:

In-beam and e- spectroscopy : up to few 100pnA ( highly segmented detectors, digital electronics,time stamping)

Cross section below 100pb will be reachable

Off-beam spectroscopy (decay studies):

up to few 100pA.

Cross section down to 1pb will be reachable

and e- spectroscopy using transfer reactionson radioactive targets with high intensity beams

(need a dedicated spectrometer: PRISMA,VAMOS)

28

8

20

50

82

82

50

288

20

126

Decay spectrsoscopy

few 100pnA

In-beam spectroscopy

With very high beam intensity and inverse kinematics,Coulomb excitation of recoils at the focal plan of the separator will be possible ( as systematic of B(E2) values carries the fingerprint of specific shell effects)

Example:With a pA primary beam, the Coulomb excitation of superheavy nuclei Produced with cross section down to the b becomes feasible

Secondary reactions at the focal plan:

• High-Intensity beams and Super-Heavy Elements

Recoil separator with high rejection power 1013-15

Target development

New generation detectors (GREAT, AGATA) with new genaration electronics and data correlation.

Long and dedicated beam time

Filter

6th PCRD -> European Collaboration

Production, secondary reactions and off beam studies: intensities of few 100pA!

In beam studies: intensities of few 100pnA!

Medium-spin studies of neutron-rich nuclei using -spectroscopy with Deep-Inelastic reactions:

With the factor 10 to 100 increase in beam intensity medium spin statesare accessible in nuclei of the regions where known neutron shell effect

are disappearing and new ones are appearing! (N=20, N=28, N=32 , N=50)

LEGNARO

Single particle migrationShell effect changes

Test experiment recently done at GASP (Z. Podoliach)Test experiment recently done at GASP (Z. Podoliach)

With few 100pnA beams Will be accessible!

Discovery of superdeformed triaxial nuclei!

Through their wobbling modes of excitation(fluctuation of the rotational axis away from the principal axis)

163Lu

Euroball IV + Vivitron S.W.Odegard et al., Phys. Rev. Letters 86 (2001) 5866 D.R. Jensen et al., Phys. Rev. Letters 89 (2002) 142503

The study of high spin states and their decay modes in heavy nuclei (many fascinating new results)!

Jacobi shape transition

Rotational damping

Hyperdeformation

ChaosAssistedtunneling

superdeformation

fission

SPIN

ENERGY GDR

Tetrahedralnuclei

A domain rich of new exotic phenomena to be discovered

Search for Hyperdeformationdedicated long experiment (VIVITRON+EUROBALL)

Rotational Plane Mapping (N=1) and after 2n filtering

Eγ2

Eγ1(keV)400 800 1200 1600 2000

Rotational Plane (δ = 12 keV) Data: 261 MeV – 255 MeV

3D Rotational Plane (δ = 12 keV)261 MeV 64Ni + 64Ni – 2 n => 126Ba

Perpendicular cut: 1440 ± 102 keV

FOLD

28+h

26+h

24+h

22+h

-400 -200 0 200 400 -400 -200 0 200 400

Eγx – Eγy Eγx – Eγy

26+h: Perpendicular cut: 1440 keV

Cut-width = 204

Cut-width = 84

Cut-width = 124

Cut-width = 164

high granularity+

digital electronics, time stampingUltra fast processing

AGATA will be able to handle

10 – 100 times more beamAdvanced GAmma Tracking Array

Important point:

For high spin physics incomplete fusion is a promising technique and will be

intensively used in the future!(fusion-reaction with radioactive beams)!!

Need a dedicated 0° spectrometer (A and Z determination of the non-fusing fragments)

A high resolving-power -array (AGATA)

HISB

The discovery of rotational bands in superdeformed light nuclei ( 36Ar , 40Ca)

40Ca

2=0.62=0.3

Offer the opportunity to look for their linkswith resonant molecular and cluster states!

and the new generation gamma arrays

32 S + 24

Mg

48

Cr

First hints!

8Be 48Cr

Déformé

Sphérique

Von Oertzen et al.

Search forSearch for transitions between highly deformed molecular states! transitions between highly deformed molecular states!Search forSearch for transitions between highly deformed molecular states! transitions between highly deformed molecular states!

12C

24Mg

12C0+

2+

4+

6+

8+

Experimental challenge! as the gamma branching ratio very small (10-5-10-6)

Needs highly efficient , highly segmented gamma array in conjunction with binary reactionSpectrometer, higher beam intensity and dedicated experiments with long period of beam time

Nuclear Structure in medium mass N=Z nuclei

Nuclear Structure in medium mass N=Z nuclei

50Fe

58Cu

64Ge

70Br67Se 88Ru

66As

21Ne

114Xe

• Coherent pn octupole correlations• Isospin mixing in N=Z=32 64Ge E1 decay in mirror nuclei 67Se• Isospin symmetries and mirror pairs• Spectroscopy at the dripline• pn pairing and delayed alignment

• Coherent pn octupole correlations• Isospin mixing in N=Z=32 64Ge E1 decay in mirror nuclei 67Se• Isospin symmetries and mirror pairs• Spectroscopy at the dripline• pn pairing and delayed alignment

~ barn

The study of high spin states in N=Z nuclei (up to 100Sn) is still (and will stay ) the domaine of experiments with stable beamsand new generation detection systems!

The response of nuclei torotation should bring valuableInformation on n-p pairing!

FUTURE:In-beam studies: AGATA+highly segmented charged particle detectors+ Recoil spectrometer,

higher beam intensity (x10 to x100) and longer beam time!

Decay studies and Coulomb excitation at the focal plan: High intensity beams up to few tens of pA

The low energy nuclear structure community has well defined and promissingresearch programs for the future. Many of them are based on measurements to be carried out using higher intensity stable beams.

The in-beam studies will benefit from the high segmentation of new detection Systems and from digital electronics, in order to allow the increase of beam intensity by one order to two orders of magnitude ( up to few 100pnA). Other approaches using detection systems after a separator (focal plan)require a stable beam facility with very high intensities ( up to 100pA)

In all the cases a dedicated detection system is needed to run experiments with longer beam time.

Existing European facilities Legnaro, JYFL (up to few 100pnA) GSI (unilac), Ganil (CSS1) (up to 1pA)Projects of very high intensity injectors for SPES and SPIRAL2 (LINAG up to 1pmA of Ar)

but not for all species

‘It is certain that even after the construction of second generation radioactive beam facilities critical measurements using stable beams will be required. Furthermore, it is almost certain that measurements and discoveries made with radioactive species will stimulate new programs requiring stable beams.’

My suggestion for you would be to have a European working group to assess the research perspectives of the existing stable beam facilities, their needs for development, their specificities or complementarities (from the point of view of the physics program). A report from this working group and its recommendations will be very useful for the community.

My personal opinion is that stable beams with moderate intensity (up to few 100pnA) for a wide range of ions should be made available, within the coming years at some of the existing stable beam facilities in order to take advantage of the ongoing detector and electronics developments. The higher intensity stable beam (up to 1pmA) should take advantage (in a way that should be discussed) of the developments of driver accelerators for the future radioactive beam facilities.